Chapter 4 Practical 2

 Chapter 4 Practical 2

 Assess air quality index (AQI) of any location using real-time air quality parameters

 Part A

 Aim:
To assess and interpret the Air Quality Index (AQI) of a chosen location by acquiring real-time air quality parameter data from a government monitoring portal, to determine the associated health implications, and to analyze the potential sources of pollution.

Principle:
The Air Quality Index (AQI) is a standardized tool used to transform complex air pollution data into a single number and colour that communicates the level of health risk to the public. It is calculated for key air pollutants that have established health-based standards (National Ambient Air Quality Standards - NAAQS in India).

1. Pollutants Measured: The AQI is typically based on the concentrations of the following criteria pollutants:

   • Particulate Matter (PM2.5 and PM10): Microscopic particles that can penetrate deep into the lungs and bloodstream.

   • Nitrogen Dioxide (NO₂): A reddish-brown gas from high-temperature combustion (vehicles, power plants), contributes to smog and respiratory problems.

   • Sulfur Dioxide (SO₂): A gas from burning fossil fuels containing sulfur (like coal), contributes to acid rain and respiratory illness.

   • Ozone (O₃): A gas at ground level formed by chemical reactions between oxides of nitrogen (NOx) and Volatile Organic Compounds (VOCs) in sunlight. It is a major component of smog.

   • Carbon Monoxide (CO): A colorless, odorless gas from incomplete combustion, reduces oxygen delivery in the body.

2. Index Calculation: The AQI is calculated for each pollutant individually using a piece-wise linear function that scales the measured concentration to the index value. The overall AQI is the highest (worst) value among these individual indices. This "one-break" rule means the pollutant with the highest AQI is the dominant pollutant driving the health message for that day.

3. Health Breakpoints: The AQI is divided into categories (Good, Satisfactory, Moderate, Poor, Very Poor, Severe), each with associated health advisories for the general public and sensitive groups.

Materials Required:

1. Computer or Smartphone: With internet access.

2. Data Source Access: Links to official air quality monitoring portals:

   • India: Central Pollution Control Board (CPCB) - https://airquality.cpcb.gov.in/AQI_India/ or https://airquality.cpcb.gov.in/ccr/#/caaqm-dashboard-all/caaqm-landing/data

   • United States: EPA's AirNow - https://www.airnow.gov/

   • Other: IQ Air AirVisual platform is a good global aggregator (https://www.iqair.com/in-en/world-air-quality).

3. Data Sheet: For recording observations (digital or printed).

4. Reference Material: AQI chart with colour codes, health implications, and suggested actions (provided below).

Procedure:

Step 1: Selection of Location and Data Acquisition

1. Choose two distinct locations for comparison (e.g., a city center/industrial area vs. a suburban/residential area; or your college campus vs. a nearby traffic intersection).

2. Access the real-time air quality data portal (e.g., CPCB's AQI India website).

3. Use the map interface or station list to find and select your first location. Ensure the data is from a continuous monitoring station (CPCB or SPCB).

4. Record the date and time of your observation.

5. Note the real-time concentration values (in µg/m³ or ppm) for all available parameters: PM2.5, PM10, NO₂, SO₂, O₃, and CO.

6. Record the AQI value and the Dominant Pollutant as reported by the portal.

7. Repeat the process for your second chosen location.

Step 2: Data Recording and AQI Interpretation

1. Transfer your data into a structured table (see Observation & Data Analysis below).

2. For each location, use the AQI chart (Table 1) to determine the AQI category and associated health impacts based on the reported AQI value.

Step 3: Analysis and Source Apportionment

1. Compare the AQI and the dominant pollutant between the two locations.

2. Analyze the concentration data. For example, if PM2.5 is high, think about sources like vehicle exhaust, construction dust, or industrial emissions. If NO₂ is high, it strongly points to vehicular traffic.

3. Correlate your findings with the time of day, day of the week (weekday vs. weekend), and known local activities (e.g., heavy traffic hours, construction nearby, industry operations).

Observations & Data Analysis:

Table 1: Standard AQI Categories and Health Implications (Based on CPCB)

AQI Category	AQI Range	Colour Code	Health Impacts
Good	0 - 50	Green	Minimal impact
Satisfactory	51 - 100	Light Green	Minor breathing discomfort to sensitive people
Moderate	101 - 200	Yellow	Breathing discomfort to people with lung disease, asthma, and heart disease
Poor	201 - 300	Orange	Breathing discomfort to most people on prolonged exposure
Very Poor	301 - 400	Red	Respiratory illness on prolonged exposure
Severe	401 - 500	Dark Red	Affects healthy people and seriously impacts those with existing diseases

Table 2: Real-Time Air Quality Data Recording Sheet

 

 

Parameter	Unit	Location 1: City Center (ITO, Delhi) *Date: 07-10-2023 Time: 10:00 AM*	Location 2: Suburban Area (Dwarka, Delhi) *Date: 07-10-2023 Time: 10:00 AM*	NAAQS Standard
PM2.5	µg/m³	145	95	60 (24-hr)
PM10	µg/m³	280	170	100 (24-hr)
NO₂	µg/m³	85	45	80 (24-hr)
SO₂	µg/m³	25	12	80 (24-hr)
O₃	µg/m³	90	60	100 (8-hr)
CO	mg/m³	1.2	0.8	4 (8-hr)
Reported AQI	---	278	168	---
Dominant Pollutant	---	PM10	PM2.5	---
AQI Category	---	POOR	MODERATE	---

Result:
The air quality assessment conducted on October 7, 2023, at 10:00 AM revealed a significant disparity between the two locations.

• Location 1 (City Center) had a Poor AQI of 278, primarily driven by high levels of PM10.

• Location 2 (Suburban Area) had a Moderate AQI of 168, primarily driven by PM2.5.
  This indicates that the city center experiences worse air quality, with coarser particulate pollution (PM10) being a major concern, likely due to higher levels of road dust, vehicle traffic, and construction activities.

Discussion:

1. Source Apportionment: The high PM10 in the city center strongly suggests sources like re-suspended road dust from vehicular movement, construction activities, and unpaved roads. The higher NO₂ levels further support the influence of vehicular emissions. The suburban area, while better, still shows significant PM2.5 pollution, which can travel long distances and originates from similar combustion sources (vehicles, industry, power plants) and secondary particle formation.

2. Health Implications: The Poor AQI at the city center implies that prolonged exposure could cause breathing discomfort for a significant portion of the population. Active children and adults, and people with respiratory or heart diseases should avoid prolonged outdoor exertion. The Moderate AQI in the suburban area suggests a lower, but still present, risk primarily to unusually sensitive individuals.

3. Limitations of the Method: This practical uses data from a single government monitoring station for each location. The actual exposure of an individual can vary significantly based on their immediate micro-environment (e.g., being inside a car in traffic, near a restaurant's chimney, or inside a park). The data is also a snapshot in time; a more robust analysis would require studying diurnal and seasonal trends.

4. Link to Policy and Mitigation: The results highlight the need for targeted mitigation strategies:

   • For PM10: Enhanced road sweeping and washing, covering construction material, and paving roads.

   • For PM2.5 and NO₂: Stricter vehicle emission norms, promotion of public transport, and transition to electric vehicles.

   • Public health advisories linked to the AQI are crucial for protecting vulnerable populations.

Conclusion:
This practical successfully demonstrated the use of publicly available real-time data to assess and interpret the Air Quality Index (AQI). The exercise confirmed that air quality is not uniform across a city and is highly dependent on local emission sources. The AQI serves as a critical tool for translating complex scientific data into actionable public health information. Understanding how to access, interpret, and critically analyze AQI data is an essential skill for informed citizenship and for future environmental professionals tasked with developing solutions to the air pollution crisis.

Viva Voce Questions:

1. Why is the overall AQI value always determined by the highest individual pollutant index?
   Because it represents the most significant immediate health threat. A high level of one dangerous pollutant is enough to cause adverse health effects, regardless of how low the other pollutants are. This "one-break" rule ensures public health advisories are based on the worst-case scenario.

2. If the dominant pollutant is Ozone (O₃), what can you infer about the time of day and the weather conditions?
   Ozone is a secondary pollutant formed by photochemical reactions. Therefore, its concentration is typically highest during the afternoon and early evening on sunny, hot, and stagnant days when sunlight is most intense, facilitating the reactions between NOx and VOCs.

3. What is the key difference between PM2.5 and PM10 in terms of health impact and source?
   PM10 (Inhalable particles) can irritate the eyes, nose, and throat. PM2.5 (Fine particles) are more dangerous as they can penetrate deep into the lungs and even enter the bloodstream, causing cardiovascular and respiratory problems. PM10 often comes from dust, pollen, and crushing operations, while PM2.5 primarily comes from combustion (vehicles, power plants, fires).

4. You notice the AQI is consistently worse in the winter months in North Indian cities. What is this phenomenon called and what are its primary causes?
   This is called wtime pollution. The primary causes are: (a) Meteorological: Lower mixing height (shallow boundary layer) and colder temperatures trap pollutants near the ground; calm winds prevent dispersion. (b) Anthropogenic: Increased emissions from biomass burning for heating and the festival of Diwali, coupled with stubble burning in adjacent agricultural states.

5. How can an individual use the AQI reading in their daily life?
   An individual can use the AQI to make informed decisions to protect their health. For example, on a "Poor" AQI day, they can: postpone a strenuous outdoor run, choose a route with less traffic for commuting, ensure windows are closed, use an air purifier indoors, and wear a well-fitted N95/99 mask if outdoor exposure is unavoidable.

    

   Part B 

    

Aim

To calculate the Air Quality Index (AQI) for a chosen location by obtaining real-time concentrations of key pollutants from a government monitoring portal and applying the official AQI calculation formula, thereby understanding the transformation of raw data into a public health tool.

Principle

The Air Quality Index (AQI) is a dimensionless number that provides a standardized way to communicate how polluted the air is and what the associated health effects might be. It is calculated for major air pollutants, each with established national air quality standards.

• Key Pollutants: Particulate Matter (PM₂.₅ and PM₁₀), Nitrogen Dioxide (NO₂), Sulfur Dioxide (SO₂), Ozone (O₃), and Carbon Monoxide (CO).
• The Calculation Method:
  The AQI is calculated for each pollutant individually. The overall AQI is the maximum of these individual index values. The formula for each pollutant is a piece-wise linear function:

Where:

 

I_p = Index for pollutant P

C_p= Truncated concentration of pollutant P

BP_Hi= Breakpoint concentration ≥ C_p

BP_Lo = Breakpoint concentration ≤ C_p

I_Hi= AQI value corresponding to BP_Hi

I_Lo= AQI value corresponding to BP_Lo

Truncation: The measured concentration (Cp) is truncated to the number of significant figures of its respective National Ambient Air Quality Standard (NAAQS) before calculation.

Materials Required

• Computer or Smartphone: With internet access.
• Data Source: Access to an official air quality data portal:
• India: Central Pollution Control Board (CPCB) - https://app.cpcbccr.com/AQI_India/
• USA: EPA's AirNow - https://www.airnow.gov/
• Calculator: A scientific calculator or spreadsheet software (Excel/Google Sheets).
• Reference Table: The official AQI breakpoint table for the country (e.g., CPCB's AQI Breakpoint table for India, provided below).
• Notebook & Pen: For recording data and calculations.

Procedure

Step 1: Data Acquisition

1. Choose a location with an active government monitoring station (e.g., "Delhi - ITO").
2. Access the real-time air quality data portal.
3. Record the current date, time, and the precise concentrations for the following pollutants from the chosen station:
• PM₂.₅ (µg/m³)
• PM₁₀ (µg/m³)
• NO₂ (µg/m³)
• SO₂ (µg/m³)
• O₃ (µg/m³)
• CO (mg/m³) Note: Units for CO are different.

Step 2: Data Truncation
Truncate (do not round) each measured concentration value to the number of significant figures specified in the NAAQS for that pollutant.

• Example: If the measured PM₂.₅ is 108.76 µg/m³, and the NAAQS standard is 60 (which has 2 significant figures), truncate it to 108 µg/m³.

Step 3: Individual AQI Calculation for Each Pollutant

1. For each truncated pollutant concentration (C_p),refer to the AQI Breakpoint Table.
2. Identify the row where C_p falls between BP_Lo and BP_Hi.
3. Plug the values (C_p , BP_Hi, BP_Lo, I_Hi, I_Lo) into the linear equation to calculate the Index (I_p) for that pollutant.
4. Round the calculated I_p to the nearest integer.
5. Repeat this process for all six pollutants.

Step 4: Determine the Overall AQI

1. Compare the calculated Individual Indices (I_p) for all pollutants.
2. The highest value among these indices is the final AQI for that location.
3. The pollutant responsible for this highest index is declared the "Dominant Pollutant".

Step 5: Categorization and Interpretation

1. Use the AQI scale to categorize the calculated AQI (e.g., Good, Satisfactory, Moderate, etc.).
2. Interpret the health implications based on this category.

Observations & Data Analysis

Table 1: CPCB AQI Breakpoint Table (Key Pollutants)

AQI Category	AQI Range	PM₁₀ (µg/m³)	PM₂.₅ (µg/m³)	NO₂ (µg/m³)	O₃ (µg/m³)	CO (mg/m³)	SO₂ (µg/m³)
Good	0-50	0-50	0-30	0-40	0-50	0-1.0	0-40
Satisfactory	51-100	51-100	31-60	41-80	51-100	1.1-2.0	41-80
Moderate	101-200	101-250	61-90	81-180	101-168	2.1-10	81-380
Poor	201-300	251-350	91-120	181-280	169-208	10-17	381-800
Very Poor	301-400	351-430	121-250	281-400	209-748*	17-34	801-1600
Severe	401-500	430+	250+	400+	748+*	34+	1600+

**Note: O₃ breakpoints are for an 8-hour average. 1-hour average breakpoints are different.*

Table 2: Data Recording and Calculation Sheet
*Location: Delhi - ITO | Date: 26-09-2023 | Time: 11:00 AM*

Pollutant	Measured Conc.	Truncated Conc. (Cp)	Breakpoints Found (BPLo - BPHi)	Index Breakpoints (ILo - IHi)	Calculated Index (Ip)
PM₂.₅	108.76 µg/m³	108 µg/m³	91 - 120	200 - 300	259
PM₁₀	280.50 µg/m³	280 µg/m³	250 - 350	200 - 300	230
NO₂	85.20 µg/m³	85 µg/m³	81 - 180	100 - 200	101
O₃	90.10 µg/m³	90 µg/m³	51 - 100	50 - 100	90
CO	1.25 mg/m³	1.2 mg/m³	1.0 - 2.0	50 - 100	60
SO₂	24.90 µg/m³	24 µg/m³	0 - 40	0 - 50	30

Sample Calculation for PM₂.₅ (Cp = 108 µg/m³):

• It falls in the "Poor" category (91-120 µg/m³).
• Thus:

                BP_{Hi =} 120

                BP_Lo = 91

                I_Hi = 300

               I_Lo  = 201

               

• Plug into the formula: 

Case 1: Particulate Matter ($P{M}_{2.5}$)

• Measured Conc: $108.7\mu g/m^3$

• Truncated ($C_p$): $108$

• Find Breakpoints (Table 1): $108$ falls between 91 and 120 (Poor Category).

  • $B{P}_{Lo}=91$, $B{P}_{Hi}=120$

  • $I_{Lo}=201$, $I_{Hi}=300$

• Calculation:

  

Round to the nearest integer:259

 

Case 2: Nitrogen Dioxide ($N{O}_2$)

• Measured Conc: $45.3\mu g/m^3$

• Truncated ($C_p$): $45$

• Find Breakpoints (Table 1): $45$ falls between 41 and 80 (Satisfactory Category).

  • $B{P}_{Lo}=41$, $B{P}_{Hi}=80$

  • $I_{Lo}=51$, $I_{Hi}=100$

• Calculation:

   

   Result: $I_p=56$ (Rounded to nearest integer).

 

 

Step 4: Determine Final AQI

Compare all calculated $I_p$ values:

• $P{M}_{2.5}$ Index: 259

• $N{O}_2$ Index: 56

• ... (Assuming other values are lower)

Final AQI: 259 Dominant Pollutant: $P{M}_{2.5}$ Category: Poor

Result

The calculated Air Quality Index (AQI) for ITO, Delhi, at 11:00 AM on 26-09-2023 is 259, which falls in the "Poor" category. The dominant pollutant is PM₂.₅.

 

Discussion

• Calculation Validation: The self-calculated AQI (259) should be compared to the value reported on the CPCB website for the same time and location. A small difference is possible due to the time-averaging of data used by the portal versus our snapshot calculation, but it should be very close, validating our method.
• Health Implications: A "Poor" AQI signifies that the air quality can cause breathing discomfort to most people, especially during prolonged exposure. Sensitive groups (people with lung or heart disease, children, older adults) should reduce heavy exertion outdoors.
• Source Apportionment: The dominant pollutant, PM₂.₅, suggests the primary sources are combustion processes (vehicle emissions, industrial activity, biomass burning) rather than coarse dust (PM₁₀), which is typically from construction and roads.
• Limitations: This calculation uses a snapshot of data. Official AQI is often based on rolling 24-hour averages for most pollutants (except O₃ and CO, which have shorter averages), which smooths out short-term spikes. Our manual calculation uses a single instantaneous value.
• Significance of the Exercise: Manually calculating the AQI demystifies how raw environmental data is transformed into a crucial public communication tool. It reinforces understanding of standards, breakpoints, and the "one-break" principle that drives health advisories.

Conclusion

This practical successfully demonstrated the step-by-step methodology for calculating the Air Quality Index from real-time pollutant concentration data. By applying the linear interpolation formula to truncated data, we accurately determined the AQI and identified the dominant pollutant. This process highlights the scientific rigor behind the simple AQI number and emphasizes its critical role in public health warning systems. Understanding this calculation is fundamental for environmental science students to critique, manage, and communicate air quality information effectively.

Viva Voce Questions

1. Why do we truncate the measured concentration instead of rounding it?
   Truncation is a more conservative approach. It ensures we do not artificially inflate the concentration value, which could lead to a higher and potentially more alarming AQI value than is strictly necessary based on the data.
2. Why is the overall AQI always determined by the highest individual pollutant index?
   This is known as the "principle of worst-case reporting." It ensures that public health advisories are based on the most hazardous pollutant present, as exposure to a single pollutant at a high level is enough to cause adverse health effects.
3. If the AQI is 300 due to PM₁₀, and the PM₂.₅ level is "Good" (AQI=45), is the air safe for a person with asthma?
   No, it is not safe. The overall AQI of 300 ("Very Poor") is driven by PM₁₀. While PM₂.₅ is low, the high level of PM₁₀ can still trigger asthma attacks and respiratory issues. The health advisory is based on the overall AQI, not the best pollutant.
4. What is the difference between the AQI and the NAAQS?
   The NAAQS are legally enforceable concentration limits set to protect public health with an adequate margin of safety. They are the raw scientific targets. The AQI is a derived, dimensionless index that simplifies these standards and their health impacts into a single number and colour code for effective public communication.
5. What might cause a diurnal (daily) variation in AQI, particularly for pollutants like NO₂ and O₃?
   NO₂ peaks during morning and evening rush hours due to high vehicle emissions. O₃ is a secondary pollutant formed by sunlight-driven reactions. Its concentration typically peaks in the afternoon when sunlight is most intense, even though the primary pollutants (NOₓ, VOCs) may have been emitted earlier in the day.